Low density paper used in transfer electrophotography

ABSTRACT

A lightweight electrophotographic copy paper having a low density bulking substance embedded in the paper fiber and a surface size comprising a salt, clay and binder composition is prepared. The lightweight electrophotographic copy paper has particular utility in electrophotographic machines because of its ability to feed properly and render non-scorched copies.

United States Patent Green, Jr. et al.

1451 May 20, 1975 LOW DENSITY PAPER USED IN TRANSFERELECTROPl-IOTOGRAPHY Inventors: Charles J. Green, Jr.; George Treier;Robert H. MacClaren, all of Webster, NY.

Assignee: Xerox Corporation, Stamford,

Conn.

Filed: Dec. 6, 1973 Appl. No.1 422,452

Related US. Application Data Division of Ser. No. 98,883, Dec. 16, 1970,which is a continuation-in-part of Ser. No. 50,886, June 29, 1970,abandoned.

References Cited UNITED STATES PATENTS 11/1962 Dalton 162/138 3,271,1469/1966 Robinson 96/].4 3,293,115 12/1966 Luckon 162/138 X 3,420,734l/1969 Anderson et al. 162/138 X 3,468,660 9/1969 Davenport et a1...162/138 X 3,486,936 12/1969 Cahill 162/138 X 3,556,784 l/197l Robinsonet al.. 96/].4 3,592,642 7/1971 Kaupp 96/l.4 3,615,403 10/1971 Cheng162/138 3,708,288 l/l973 Lin 96/l.4 3,811,914 5/1974 Saito et al 96/l.4X

OTHER PUBLICATIONS Casey, Pulp and Paper, vol. 3, lnterscience N.Y 1961,pp. 1552-1554, 1570, 1571, 1592, 1593.

Primary ExaminerRoland E. Martin, Jr.

[57] ABSTRACT A lightweight electrophotographic copy paper having' 3Claims, No Drawings LOW DENSITY PAPER USED IN TRANSFERELECTROPI-IOTOGRAPHY RELATED APPLICATIONS This is a division ofapplication Ser. No. 98,883, filed Dec. 16, 1970, which is acontinuation-in-part of our co-pending application, Ser. No. 50,886,filed on June 29, 1970, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to an improvedelectrophotographic copy paper. It more particularly relates to animproved electrophotographic copy paper containing small resinousparticles.

Paper has many uses in packaging, printing, preparation of containers,and the like. One of the basic shortcomings of conventional paper is itsweight. Relatively high density of paper imposes a significantfinancial.

burden in shipping, mailing, and the like. For example, magazines, whenprinted on a paper which is sufficiently dense and thick to give thereader the impression of quality, generally weighs considerably morethan is necessary if the minimum thickness of paper were used whichwould permit readability. Frequently among the thicker papers oftenreferred to as paper board or box board, a relatively high weight isrequired to obtain the desired thickness and stiffness. In manyinstances, such as in the preparation of paper cups, conventional papersdo not have a sufficient insulating value for use as hot cups unless anexcessive quantity of pulp is employed.

In U.S. Pat. No. 3,293,114 to Kenaga et al., there is disclosed aproduct which overcomes the shortcomings of conventional paper. Morespecifically the aforementioned patent sets forth the preparation of alightweight paper by incorporating a plurality of synthetic polymericparticles, having a generally spherical shape and defining a generallyconcentric spherical cavity, into paper fibers. The preparation includesthe addition of from about 0.05 to 60 percent of the spherical polymericparticles, having a diameter of from about 0.5 to 200 microns, to a pulpslurry. The resulting paper product is characterized by its lightweightand excellent stiffness characteristics.

Another means of rendering paper lightweight is described in U.S. Pat.No. 3,210,239 issued to Eberl etal. This patent describes a bulked paperproduct which contains angulate fibrous fragments of foamed aminoplastresins as the bulking material. The preparation of the lightweight paperincludes adding up to about 50 percent by weight of a disintegratedaminoplast resin to a pulp slurry before production of paper sheets. Thepaper product is characterized by a low densitycompared to paper usingwood pulp alone.

In the art of electrophotography, paper is an important consumable inthat it is used in all electrophotographic copiers. While thelightweight papers demonstrated in U.S. Pat. Nos. 3,293,114 and3,210,239 obviate many of the problems presented by conventional paper,more peculiar needs exist in the use of-a lightweight paper as a mediumfor electrophotographic copying. Therefore, while there is a need for alightweight paper for use in electrophotography, certain problems existas to its physical and electrical properties with regard to use inmachines. For example, if

such a paper has too high a curl it will cause jamming as its proceedsfrom the feederthrough the electropho tographic machine, Likewise, ifthe paper either has a high coefficient of friction or accumulateselectrostatic charges at its surface, sheets of the paper will stick andwill not properly feed into the electrophotographic machine.

It has been found that the difficulties as set forth above, exist whenutilizing a paper which has been rendered lightweight by the addition ofbulking substances. For example, lightweight paper containing gaseousthermoplastic resin spheres exhibits strong tendencies to curl whichproperty causes the paper to wrap about the roll feeders of the machineand thereby jam it. In addition, the preparation of thisresinous-gaseous filled-sphere paper results in the spheres beinglocated at or upon the surface of the paper fibers. Being in such aposition the polymeric spheres create a high coefficient of friction forthe surface of the paper which high friction property further ultimatelyresults in an undesirable electrostatic buildup. This gaseous filledthermoplastic resin filled lightweight paper, because of its undesirableelectrostatic and frictional properties, is

essentially non-functional in friction type paper feeders which arefound in conventional electrophotographic equipment. Therefore, becauseof the surface presence of the polymeric spheres the lightweight paperwill retain such high electrostatic charges that it will misspuff inmachines using photoreceptor drums; that is, the paper will stick to thephotoreceptor drum and fail to exit.

The same disadvantages encountered in using lightweight paper containingthermoplastic gaseous filled resinous spheres in electrophotographiccopying appear when the lightweight paper contains other materials forbulking purposes. For example, when using aminoplast thermosettingresins as a bulking material for paper, as taught in U.S. Pat. No.3,210,239, the paper has inadequate curl, surface friction, anddiscoloration for use in electrophotographic copying. And further, whenusing natural polymeric substances such as cellulosics, cellulosederivatives, and proteins as bulking substances, the lightweight paperis found inadequate for electrophotographic purposes. The reason for theshortcomings of these types of bulking materials appears to be the sameas that of the gaseous-filled synthetic resins in that the bulkingsubstance appears at the surface of the paper thereby rendering itunusable in electrophotography.

These particular characteristics of bulked lightweight paper are soserious that when used in an electrophotographic machine malfunctionswill occur as often as one sheet in ten and sometimes even more often.In addition, resulting copies are of poor quality due to a slightdiscoloration. While it might be expected that surface sizing wouldobviate the aforementioned .difficulties, the addition of conventionalsurface sizes having ordinary salts in a concentration of from about 1to 5 percent are not generally found useful because the bulkingsubstance is still left exposed at the surface and will still causetheproblems outlined above. In addition, the use of ordinary salts insurface sizings will cause increased tendency for the paper to scorch ordiscolor when tonerfusing is accomplished by radiant or pressure fusing.

OBJECTS OF THE lNVENTlON Therefore, it is an object of this invention toprovide 1 a lightweight electrophotographic copy paper.

It is a further object of this invention to provide a lightweightelectrophotographic copy paper having a surface sizing which renders thepaper useful in electrophotographic machines.

Another object of this invention is to provide a lightweightclectrophotographic copy paper having excellent curl and frictioncharacteristics for use in electrophotographic machines.

Still another object of this invention is to provide a preparation of alightweight electrophotographic copy paper.

DESCRIPTION OF THE INVENTION These benefits and other advantages inaccordance with the present invention are achieved in the preparation ofan electrophotographic copy paper by incorporating into said paper a lowdensity bulking material, and subsequent surface sizing of thelightweight paper to render it useful in electrophotographic machines.Electrophotographic copy papers in accordance with the present inventionare more readily prepared by the addition of up to about percent of thelow density bulking material, based upon the weight of the dry pulp, tothe pulp slurry. The resulting lightweight paper is then surface sizedwith a composition comprising a binder, a salt, preferably in amountsfrom about 1 to 50 percent by weight based upon the amount of binder,and 40 to 50 percent clay based on the total coating composition, butsuch that the combination of salt and clay does not exceed 60 percentbased on the total coating composition.

The particular binder to be used in the surface sizing composition isnot critical to the electrophotographic copy paper of the instantinvention. Therefore any commercially available binder productsconventionally used in surface sizing compositions may be used. Typicalbinders include starch, starch derivatives, polyvinyl alcohol.polystyrene, and mixtures thereof. Because of its anti-scorchproperties, polystyrene latex in a weight ratio of from about 40 percentor more is a particularly useful binder in the sizing of the presentinvention.

The particular salt to be used in combination with the binder in a ratioof from about 1 to 50 percent by weight can be any salt which incombination with the binder yields a surface sizing which imparts to thelightweight paper the properties of scorch resistance, improvedconductivity, and strength retention under conditions of heating.Preferable salts within the purview of the present invention include thesulfate salts of any metal. Typical salts of this group which giveexceptional results are magnesium sulfate, zinc sulfate and sodiumsulfate and the hydrates thereof.

Any type of coating clay known to those skilled in the art may be usedwithin the purview of the present invention. The only requirementrelating to the clay composition is the amount present in the surfacesize. As mentioned above, the clay should be present in an amount offrom about 40 to 50 percent by weight based on the total composition,but such that the combination of salt and clay does not exceed 60percent by weight.

While the binder, salt and clay surface sizing of the present inventionhas been described with respect to the three major components, itis'well understood to one skilled in the art that many additives can beused in the binder salt composition. For example, wetting agents can beadded in order to improve the application of the. surface coating.

As heretobefore mentioned, the lightweight electrophotographic copypaper of the present invention contains from up to about 10 percent ofbulking material. For optimum properties for use in electrophotographicmachines the paper should comprise over percent cellulose fiber to avoidroughness in the paper surface. Therefore, the lightweight paper of theinstant invention preferably should contain from about 0.5 up to 5percent bulking material.

The particular material used for bulking the paper is not criticalwithin the purview of the present invention and may be synthetic resinsof the type described in U.S. Pat. Nos. 3,293,114, 3,210,239, 3,128,478,2,929,106, and 2,797,201. Natural bulking substances, such as foamedstarch and cellulosic materials, can be used with similar results. Inaddition, inorganic bulking substances such as hollow glass, ceramic andmetal microspheres can be used.

In the preparation of the lightweight electrophotographic copy paper ofthe instant invention, it is found that bulking material accumulates onthe surface of one side of the paper. In this condition the coefficientof friction of that particular side of the paper is very high.

Therefore, while not a requirement in the preparation of theelectrophotographic copy paper of the present invention, it ispreferable to subject the side of the paper having the bulking materialon its surface to a mechanical rubbing treatment with a cotton fabricmaterial before the step of surface sizing whereby flattening, abrading,or breaking of the excess bulking material occurs at the surface of thepaper. By means of the mechanical treatment of the paper those loose orprotruding particles of bulking material are removed or broken therebyrendering the subsequent surface size more effective.

EMBODIMENTS OF THE INVENTION In one general embodiment of the instantinvention, an aqueous pulp slurry is prepared and about 3 percent byweight, based on the dry pulp, of Saran microspheres, which are gaseousfilled thermoplastic resin particles produced by the Dow ChemicalCompany of Midland, Michigan are added to the slurry. The pulpresincomposition is then fed into a paper making machine which sequentiallyforms a paper sheet of the pulp fibers and applies a surface sizecomposition comprising 12 percent sodium sulfate, 38 percent clay and 50percent ethylated starch in an aqueous dispersed solution. There resultsa lightweight paper which functions properly as copy paper inelectrophotographic machines and shows no indication of discoloration.

In electrophotographic machines, the novel lightweight copy paper iscoordinated in the ordinary electrophotographic process of charging anelectrophotographic plate, imaging the charged plate with activatingradiation, developing said image with electroscopic marking particles,and transferring said image by heat or pressure fixing to thelightweight copy paper of the instant invention. The conventionalelectrophotographic process is fully detailed in U.S. Pat. No. 2,297,691to C. F. Carlson.

Having described the invention above, the following examples are givento more fully illustrate specific embodiments thereof. The examples aregiven for illustrative purposes only and are not intended to be limitingon the scope of the invention. In the examples all parts are by weightunless otherwisespecified.

EXAMPLE I An electrophotographic copy paper according to the presentinvention is prepared by the following technique:

A surface sizing is prepared by adding 100 parts by weightof Penford Gum280, an ethylated starch manufactured by the Penick and Ford Company ofCedar Rapids, Iowa, 50 parts by weight Vino] 125, a polyvinyl alcoholmanufactured by the Air Reduction Chemical and Carbide Co. of New York,New York, and 18 parts sodium sulfate to 1500 parts of water. A 220parts by weight pre-dispersed clay solution, made with Nuclay,manufactured by Freeport Kaolin Co. of New York, New York, which wasprepared by adding enough clay to water to obtain a 60 percent solidsmixture, is then added to the coating composition.

A slurry is prepared by adding 1000 lbs. of dry softwood kraft fiber,manufactured by the St. Regis Paper Company of New York, New York, 500lbs. of hardwood kraft fiber manufactured by the International PulpSales Co. of New York to 50,000 gallons of water in a hydrapulper. Thefiber is refined to a 350 Canadian Standard Freeness in a Jordan.Thereafter 90 lbs. of Experimental Resin CX 705 8-,] which are gaseousresinous spheres manufactured by the Dow Chemical Company of Midland,Michigan, are added to the slurry. The slurry is diluted to 0.5 1percent by weight of fiber and then fed into the head box ofaFourdrinier paper machine. The resulting paper passes through the dryersand at the size press the above prepared sizing composition is appliedto the paper. The sized sheet is then dried and very lightly calendcred.

The resulting surface sized lightweight electrophotographic copy paperis cut to fit a Xerox 720 machine. A stack of 200 sheets are then placedin a Xerox 720 machine and set to copy a standard pattern 200 times.There is no jamming of the machine and all 200 copies are of excellentquality demonstrating no discoloration.

EXAMPLE ll A urea-formaldehyde foam (0.8 lb/cubic foot, l5O micron celldiameter) manufactured by the DuPont Corporation of Wilmington, Delawareis pulverized in an Abbe mill with a one-sixteenth inch screen plate.Discrete amounts of the disintegrated foam are then blended with aslurry of 1000 lbs. of dry softwood kraft fiber, 500 lbs. of hardwoodkraft fiber, and 5,000 gallons of water, the slurry being prepared inthe same manner as Example I. A total of about 2 percent by weight ofthe disintegrated thermo-setting resin material is added to the slurry.The slurry is then diluted to about 1 percent by weight of fiber and asized sheet prepared in the same manner as Example I using the samesizing composition. The resulting lightweight paper is tested in a Xerox720 machine in the same manner as Example I with the same advantageousresults.

While the invention has been described in terms of preferredembodiments, it is to be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the true spirit and scope of theinvention. In addition, many modifications may be made to adapt aparticular situation or material to the teaching of the inventionwithout departing from its essential teachings.

What is claimed is:

l. A method of electrophotographically copying comprising:

a. charging an electrophotographic plate;

b. exposing the charged electrophotographic plate to activatingradiation to create an electrostatic image;

0. developing the resulting electrostatic image with electroscopicmarking particles; and

d. transferring said developed image to an electrophotographic copypaper comprising paper making fibers having incorporated therein a lowdensity bulking material in a proportion of up to about l0 percent byweight of the paper making fibers, and a surface size on said bulkedpaper having a composition comprising binder material, a metallicsulfate salt which imparts conductivity to the paper, in an amount offrom about 1 to 50 percent by weight based on said binder, and clay inan amount of from about 40 to 50 percent of the total composition, thecombination of salt and clay not exceeding 60 percent of the totalcomposition.

2. The method of claim 1 wherein the transfer step takes place'by heatfixing.

3. The method of claim 1 wherein the transfer step

1. A METHOD OF ELECTROPHOGRAPHICALLY COPYING COMPRISING: A. CHARGING ANELECTROPHOTOGRAPHIC PLATE; B. EXPOSING THE CHARGED ELECTROPHOGRAPHICPLATE TO ACTIVATING RADIATION TO CREATE AN ELECTROSTATIC IMAGE; C.DEVELOPING THE RESULTING ELECTROSTATIC IMAGE WITH ELECTROSCOPIC MARKINGPARTICLES; AND D. TRANSFERRING SAID DEVELOPED IMAGE TO ANELELCTROPHOTOGRAPHIC COPY PAPER COMPRISING PAPER MAKING FIBERS HAVINGINCORPORATED THEREIN A LOW DENSITY BULKING MATERIAL IN A PROPORTION OFUP TO ABOUT 10 PERCENT BY WEIGHT OF THE A PROPORTION OF UP TO ABOUT 10PERCENT BY WEIGHT OF THE PAPER HAVING A COMPOSITION COMPRISING BINDERMATERIAL, A METALLIC SULFATE SALT WHICH IMPARTS CONDUCTIVITY TO THEPAPER, IN AN AMOUNT OF FROM ABOUT 1 TO 50 PERCENT BY WEIGHT BASED ONSAID BINDER, AND CLAY IN AN AMOUNT OF FROM ABOUT 40 TO 50 PERCENT OF THETOTAL COMPOSITION, THE COMBINATION OF SALT AND CLAY NOT EXCEEDING 60PERCENT OF THE TOTAL COMPOSITION.
 2. The method of claim 1 wherein thetransfer step takes place by heat fixing.
 3. The method of claim 1wherein the transfer step takes place by pressure fixing.